1. Field of the Invention
The present invention relates to a method of manufacturing a nitride semiconductor based light-emitting device and a nitride semiconductor based light-emitting device manufactured by using the same.
2. Description of the Related Arts
Studies have been intensively made for implementation of a light-emitting device at parts from green to ultra-violet by the use of a semiconductor made of nitride typified by gallium nitride.
In general, a nitride semiconductor is made to grow on a substrate made of a sapphire single crystal, Si or the like by metal-organic chemical vapor deposition (abbreviated as “MOCVD”) or molecular beam epitaxy (abbreviated as “MBE”). The MOCVD has been principally used in crystal growth for a light-emitting device requiring both of N- and P-type conductive semiconductor layers.
In the case where a P-type conductive nitride semiconductor is obtained by the MOCVD, Mg has been generally used as a dopant. However, it has been known that hydrogen is mixed into a crystal of the nitride semiconductor together with Mg, to thus passivate an acceptor in combination with an Mg atom in the crystal, by an influence of a hydrogen gas used as a carrier gas during growth or a hydrogen impurity produced by decomposition of ammonia (NH3) as a raw material of nitrogen.
Such an influence has considerably reduced a carrier concentration of the resultant P-type nitride semiconductor with a high resistivity immediately after the growth.
As means for solving the above-described problem has been heretofore disclosed a technique for eliminating the hydrogen from the crystal so as to activate an acceptor and reducing a resistivity of a P-type nitride semiconductor by allowing an Mg doped P-type nitride semiconductor (GaN) to grow, followed by annealing at a temperature of 400° C. or higher (see Japanese Patent Application Laid-open No. 183189/1993).
Japanese Patent Application Laid-open No. 183189/1993 has disclosed a preferred embodiment, in which in reference to a graph illustrating the relationship between an annealing temperature and a resistivity rate of the Mg doped P-type GaN, the resistivity rate starts to gradually decrease at an annealing temperature of 400° C. or higher, most decreases at about 700° C., and continues to be at a low level up to 1000° C.
With the technique disclosed in Japanese Patent Application Laid-open No. 183189/1993, the annealing has needed to be performed at a temperature as high as at least 700° C. to 1000° C. in order to obtain the P-type GaN having a high carrier concentration.
However, a study made by inventors of the present application has showed that resistivity rate increases conversely if annealing is carried out at a temperature of 700° C. or higher. Therefore, there is not obtained the same effect as that produced by the technique disclosed in Japanese Patent Application Laid-open No. 183189/1993.
Otherwise, a technique has been disclosed, in which a catalyst metal such as Pt (see Japanese Patent Application Laid-open No. 186605/1999), Co (see Japanese Patent Application Laid-open No. 145518/1999), Pd (see Japanese Patent Application Laid-open Nos. 177134/1999 and 354458/1999), Ni (see Japanese Patent Application Laid-open No. 26389/2002) or the like is thinly formed on an Mg doped P-type nitride semiconductor in the same manner as described above, followed by annealing at a temperature of 200° C. or higher in gas containing oxygen or gas not containing oxygen, a hydrogen impurity is eliminated from a crystal, thereby increasing a carrier concentration.